TNF

      TNF is secreted by astrocytes and absorbed by neurons. It is free to diffuse throughout the environment.

Secretion

      Astrocytes secrete TNF into the same grid space at which they are located based on the amount of IL-1B they have in storage, s. Adjusting for the astrocyte concentration parameter, q, secretion occurs as long as s is greater than

q*kd*g,
where kd is the IL-1B receptor equilibrium constant for astrocytes and g is the triggering IL-1B equilibrium factor for TNF. The rate of secretion is the product of the TNF secretion rate, u, and the astrocyte concentration, q, so that
r = q u.
Because secretion occurs on the micro time scale, the increase of TNF, DS, in the grid space of the astrocyte agent satisfies
DS = dt*q*u.
Currently, there are no limits to how much IL-6 can be in any one grid space.

Diffusion

      TNF diffuses according to the diffusion properties discussed above. Initially, the diffusion coefficient equals the diffusivity parameter throughout space. However, astrocyte blocking may reduce the diffusion coefficient in specific regions.


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